Field of the Invention
The present invention relates to a method of manufacturing hexagonal ferrite magnetic powder, and more particularly, to a method of manufacturing hexagonal ferrite magnetic powder which can readily achieve a highly-dispersed state in a magnetic layer-forming coating material of a magnetic recording medium.
The present invention further relates to a magnetic recording medium having a magnetic layer comprising hexagonal ferrite magnetic powder obtained by the above manufacturing method, and to a method of manufacturing the same.
Discussion of the Background
In recent years, the means of rapidly transmitting information have undergone considerable development, permitting the transmission of data and images containing immense amounts of information. With this improvement in data transmission technology has come the demand for higher density recording in recording media and recording and reproduction devices for recording, reproducing, and storing information. The high dispersion of microparticulate magnetic powder and increased smoothing of the surface of the magnetic layer to reduce spacing loss are known to be effective ways of achieving good electromagnetic characteristics in the high-density recording region.
Reference 1, Japanese Unexamined Patent Publication (KOKAI) No. 2004-30828, which is expressly incorporated herein by reference in its entirety, for example, proposes a method of increasing the dispersibility of magnetic powder by wet dispersing hexagonal ferrite magnetic powder along with a surface treatment agent with a pKa of 1 to 4. In Reference 1, the surface treatment agent is a strong acid with a lower pKa than that of the fatty acids employed in the magnetic layer, causing adsorption to the magnetic particle surface and enhancing dispersion.
In the method specifically described in Examples of Reference 1, during the preparation of hexagonal ferrite magnetic particles by the glass crystallization method, microcrystals that are obtained by removing the glass component by acid treatment are washed with water and then subjected to the above wet dispersion. Following wet dispersion, the magnetic powder settles out in an aqueous slurry, and is collected by concentration, dehydration, and drying. Since a considerable load is then required to pulverize the magnetic powder thus solidified and to disperse it in microparticulate form, there is a risk of the magnetic powder being damaged by the dispersion medium.